Wheel Bearings :

Wheel bearings perform two very important jobs in a vehicle's suspension. They allow the wheels to rotate with minimal friction, and they support the vehicle's weight. To do both jobs, the bearings must be in near-perfect condition. The seals must also be leak-free, too, to keep the lubricant inside the bearings and contaminants out.

In a typical 3,400-lb. sedan, each pair of front-wheel bearings, as well as the rear-wheel or axle bearings, support 850 pounds depending on the front-to-rear weight distribution of the car. If we're talking a big 6,000-lb. SUV, each bearing carries about 1,500 pounds. It's a lot of weight to support for tens of thousands of miles.

Though most wheel bearings are engineered to last 150,000 miles or more, the constant load takes a toll on the bearings, the grease and the seals. A wheel bearing may fail prematurely as a result of misadjustment (in the case of serviceable bearings), contamination or loss of grease. The seals are the most vulnerable part of the wheel bearing assembly, and once a seal starts to leak, the bearings are in trouble. A worn or damaged grease seal can allow grease to leak out of the bearings, and dirt and water to enter the bearing cavity. Unless somebody discovers and corrects the problem almost immediately, the bearings are doomed.

The first symptom of wheel bearing trouble is usually noise. A rumbling, growling, chirping or cyclic noise of any kind from the vicinity of the wheels is a good indication that trouble is brewing and immediate attention is needed. If ignored, a noisy wheel bearing may suddenly fail, sometimes with potentially deadly consequences if the vehicle loses a wheel! Maneuvering a three-wheeled vehicle at highway speeds is a feat best left to a trained stunt driver. So if you think you hear a funny noise coming from a wheel, the bearings should be inspected without delay.